The invention relates in a general way to the construction, operation and maintenance of working storages incorporated into data processing systems and concerns more specially a device for locating faults in such storage.
Working stores, that is stores in which data can be written in or read out at will, constitute an essential element of data processing systems. In a great measure, working stores determine not only the capacity but also the speed and reliability of such systems. Up to the present, these working stores generally have consisted of magnetic toroidal cores arranged at the nodes of a matrix array and linked with addressing circuits, as well as circuits for writing in and reading out data. Since each core can only store one bit of information, the capacity of the storage was directly related to the number of cores it contained; hence, a large capacity store had a great number of cores and circuits. Such a store was difficult and costly to manufacture, because the cores were made as small as possible in order to reduce the size and increase the operating speed of the storage.
In order to overcome the drawbacks of magnetic toroidal core storages, it was suggested to make working stores using discrete active components, such as transistors. This solution led to very complex cabling and to a large power requirement without appreciable gains in overall size and speed. Discrete active components were rapidly superseded by integrated circuits and particularly monolithic large scale integrated circuits, each one of which comprises on a minute chip a large number of active components and hence of storage locations, as well as internal routine and operating circuits which considerably reduce the number of external connections. For example, an integrated circuit currently used for the construction of working stores and comprising 1024 locations comes in the shape of a silicon chip of a few square millimeters area sealed into a flat case not longer than 2 cm and provided with less than 20 external connections; because of the compactness of such integrated circuits, their operation is extremely fast and allows access to any storage location within a fraction of a microsecond; furthermore because a small number of connections gives access to very many locations, a large capacity storage can be easily made up by using several identical integrated circuits mounted on a printed board of small size and of relatively simple layout. This solution has, notably, the advantage of allowing the easy exchange of any defective integrated circuit. Due to their intrinsic complexity and difficult manufacturing, large scale integrated circuits, including MOS type (Metal Oxide Silicon) circuits, are subject to faults liable to detrimentally affect the operation of working stores incorporating such circuits. It is therefore important to provide a technique for identifying with ease the location of any faulty storage position and the location of the corresponding integrated circuit in order to replace the component.
The invention has as one object an arrangement for locating faults in a working storage essentially made up of identical interchangeable components, such as MOS type integrated circuits, each having several addressable locations at which at least one bit of data can be stored.
In accordance with a known and preferred layout, the components of such a storage are arranged in a matrix form in which the components of a same column correspond to a same block and those of a same row to a same data bit or group of data bits; in a corollary way the store possesses facilities for addressing simultaneously locations of a same address of all the components, circuits for the simultaneous validation of the components of a same block, parallel data input and output circuits connected respectively to storage locations corresponding to a same bit of the components of every row and facilities for selectively operating the writing or reading of a word at the specified address of the components of the validated block.